Uncle Rod's Astro Blog

A quiet little spot where Rod Mollise shares his adventures and misadventures...

Sunday, March 26, 2017

Issue #536: Deep Sky Imaging in Seven Easy (Sorta) Steps

All those cables!

We’ve spent the last several weeks setting you up with a
telescope, mount, camera, and guide system. Now it is finally time to get outside with all
that gear (assuming you, unlike me, have clear skies) and use it to capture the
deep sky wonders of Spring.

Step One: Set Up

Naturally you’ve got to assemble the telescope and mount. But
where should you assemble them? Unless your backyard is really, really horrible
light pollution wise, I strongly council you to use the good, old back forty
the first couple of times you work with the new gear. You’ll be dealing with a
bunch of unfamiliar equipment and some complex tasks, and it’s always easier to
do that at home where you can run inside for a look at a manual (or for a quick
drink if you get really stressed) under white light rather than squinting at
the instructions with a red flashlight at a dark site.

Anyhow, set up tripod and mount and level them. How precise
does level need to be for a German equatorial? Technically, you don’t have to
level the mount at all. All it needs
is to be level enough so that it doesn’t tip over. In some cases, being close to level can make
polar alignment easier, however. Level won’t affect polar alignment, period, but
being near level means the mount’s altitude and azimuth adjusters won’t
interact. When you move in altitude, it doesn’t also affect azimuth, and
vice-versa, making it quicker to dial in alignment.

Next, attach the counterweight(s) to the declination shaft. Always mount the weights first, followed by
the telescope. You will be mighty unhappy if you do the reverse, your R.A.
lock isn’t secure, and the telescope slams into the tripod. When tearing down
at the end of the run, reverse that. Remove the telescope first, then the
weights. Once the scope is safely on the mount, install everything you’ll be
placing on the tube: guide-scope and
camera, imaging camera, finders, etc.

Balance is very important if an inexpensive GEM is to track
well, so spend enough time with that to get it exactly right. First, decide
which side of the Meridian you’ll be imaging on, east or west, and balance
accordingly. You’ll always want to be slightly east heavy. If you are going to
be imaging on the West side of the Meridian, you should be “scope heavy.” On
the east side? “Counterweight heavy.”

Polar alignment with Sharpcap...

Balance in R.A. first. Point the scope north, lock the
declination lock and, with the counterweight down and halfway up the shaft (if
you don’t know approximately where it should be), undo the R.A. lock at least
partway and move the mount in R.A. so the counterweight bar is level. Do not
let go of the scope. Now, still without completely letting go, allow the scope
or weight to rise or sink. When you’ve determined which way the weight needs to
go on the shaft, up or down, return the mount to counterweight down position,
lock the R.A. lock and move the counterweight as required. Return the mount to
counterweight bar level, and see if balance is perfect. Keep on going with this
procedure until it is.

Now for the East heavy bit. When you are in perfect balance,
move the weight about ½-inch up the shaft if you are imaging to the west, and
½-inch down the shaft if you are imaging to the east. That should be more than
enough to ensure the R.A. gears remain
constantly meshed in the interests of good tracking.

For declination balance, return the mount to the
counterweight bar level position, lock the R.A. lock and, holding on to the
telescope, release the declination lock. When you know which way the scope
needs to go in the mount saddle, forward or back, return to the counterweight
down position, move the scope (carefully) as required return to the
counterweight bar level position, and check. Keep going till the scope is
balanced in declination.

What if your mount, like many in this class, is a little
stiff on the declination axis and is somewhat difficult to balance? Don’t worry
about it too much. Your mount is not tracking in declination, and if you’ve
done polar alignment well, PHD shouldn’t have to issue many guide corrections
on that axis. Good R.A. balance is far more important; declination balance can
be “approximate” without hurting anything.

Step Two: Polar Alignment

If you are using a polar alignment borescope, Polemaster,
Sharpcap, or the Kochab’s Clock method, do polar alignment now. None of these
methods require the scope to be powered up and tracking, so it’s convenient to
do the polar alignment before the mount is all festooned with cables and hand
controls (I use Sharpcap these days). Take your time and do as good a polar
alignment as you possibly can; you’ll thank me later.

Step Three: Hooking Up

Connecting to the mount...

Plug in all the cables and the telescope’s hand control. You’ll
have at least four and maybe five cords to deal with: Power cable, serial cable for scope control,
imaging camera USB connection, guide camera USB connection, and an ST-4 cable
if you’re going to guide through the mount’s auto-guide port. Try to do a neat
job with the cords, arranging them so they are not prone to snagging on the
mount or tripod—which will ruin your guiding. Don’t forget to attach dew heater
strips, dew heater controller, and dew shield if you need them in your
environment.

Step Four: Goto Alignment

Take care of goto alignment now. Do whatever procedure is
required to get the mount going to its gotos. How exactly do you line up the
alignment stars, though? You can choose one of two methods. You can either
remove the camera from the telescope and temporarily replace it with diagonal
and eyepiece, or you can use the camera to do the alignment. In the beginning,
it may be easier to remove the camera and do the goto alignment with an
eyepiece.

If you do use the camera, you’ll, of course, need to turn it on (and
the laptop and its software if you are tethering to a PC), and center the alignment stars on the
camera’s display or the laptop screen. Since alignment stars are bright, one
will allow you to get rough focus, too.

If you choose to use Celestron’s AllStar Polar Alignment, which
is built into the hand control firmware, take care of that once goto alignment
is done—ASPA requires the goto alignment be accomplished first. If you do a declination
drift polar alignment (horrors), now is also the time to do that, since having
the telescope tracking during the procedure makes things much easier and is
practically required.

Step Five: Focus

The Double Cluster is an easy and pretty target...

If you goto aligned using the DSLR, you’ve got focus roughed
in, and can now do a fine focus procedure. If you used an eyepiece instead of
the camera, however, get rough focus with the imaging camera at this time. If
the last alignment star was a good, bright one, stay on it and use it to focus.

To get in the focus ballpark, adjust the focuser on the telescope (I
am a big fan of remote moto-focus for imaging) until the bright star is as
small as you can make it and dimmer field stars begin to appear and sharpen.
Exposure? I like one to two seconds; that allows me to see results quickly
after tweaking focus. Set camera ISO as high as needed to get a good image of
the stars. If you are way out of focus, you may need to max ISO out and
increase exposure time till you detect the big round globe of a star (in a
refractor). Once it is closer to focus, back off on ISO and exposure for a less
overexposed star image.

When the field stars are as small as possible by eye, tweak
focus with a fine-focus method of choice, which may be a Bahtinov focus mask, or a focusing routine built
into imaging software (like Nebulosity) if you are tethering the camera.

Step Six: Acquire Target and Compose Shot

Rough focus done, I interface my planetarium program
(Stellarium these says) to the GEM. I start Stellarium (or whatever), and
connect it to the telescope mount, that is. How? I invariably use the ASCOM
telescope driver system, even if the program on the laptop, like Stellarium,
has built-in telescope drivers. Why? Because ASCOM includes a little onscreen
telescope HC that allows me to move the mount (at different rates) from the computer.
That means I don’t have to get up and walk out to the scope and HC, press a
direction button to center the object, walk back to the computer, etc.

A Bahtinov Mask makes fine focusing easy...

Alright, time to get on our first subject. What should that
be? Even if you are at least somewhat experienced in deep sky imaging, begin
with something easy with this new rig. This time of year, perhaps a nice winter
open cluster over in the west like M35 or M37 or the Double Cluster. One
important consideration given the economical mounts we’re using? Stay away from the Meridian. These GEMs
just don’t track well in that area. Don’t image an object that will come within
10-degrees of the Meridian before your sequence is done, and don’t begin
imaging an object until it is at least 10-degrees past the Meridian.

Once the scope goto stops, take an exposure long enough to reveal your target to see how
the composition of the shot looks. If the subject is not centered, or just not
framed the way I want it, I use the ASCOM HC to fix that. I keep the exposures short
enough to make framing easy, maybe referencing a bright star in the frame if
the object doesn’t quite show up in 1 – 3-second shots.

What if the target object is not in the field of the camera at all when the goto slew is done? That’s not much of a concern these days for most mounts,
but if you have a problem, a quick solution is to slew to a nearby bright star,
center it with the aid of your finder and “sync” on it. You should then be able
to slew back to the target and have it in the frame. Oh, before you do that, be
sure it really isn’t in the frame. If
the target is a dimmer one, increase exposure and ISO and see if it appears.

When the subject is properly centered fire up PHD2 and get
auto-guiding going. The main gotchas there? Make sure the guide scope is
well-focused and that the guide star you’ve chosen is neither too dim nor too
bright (saturated). When you put the cursor on a star, PHD2 will tell you all
about that. Some imagers believe the guide star should be slightly out of focus
for best guiding, but I’ve found I get better results from sharp stars.

When the mount is guiding, I go back to the imaging camera
and do a test exposure. How long should that test subframe be? That depends on
the sky and the subject. If I’m in the backyard, going much beyond a minute
causes the background sky to brighten up so much that processing can be
difficult later. At my dark site, I’ll expose for 2 – 5-minutes. Exposure also
depends on the subject. An open cluster like M37 will be just fine in 30-second
– 1-minute subs. The Horsehead Nebula will not be.

One important thing to remember is that while you’ll be
stacking many shorter sub-frames into a finished exposure, you still have to
have each individual exposure long enough to pick up all the detail you need.
Stacking subframes will make the final result smoother and less noisy, but will not show any detail not present in
the individual subframes. Longer subframes are always better.

Get your guiding going on...

What should camera ISO (nee “ASA”) be set to? Normally, use
as low a value as you can to capture the detail you want while keeping noise
down. The higher the ISO, the noisier the image will be (and the brighter a
light polluted background). I rarely go above ISO 1600, and try not to exceed
800 in the backyard if possible. Naturally, ISO and exposure time interact. In
general, I’ve found it better to go with a lower ISO and a longer exposure when
possible.

Also examine the test exposure for signs of star trailing.
Assuming PHD is not going wacky on you, you’ve got a good polar alignment, and
the seeing is OK, that should not be a problem at the 400 – 600mm focal lengths
we’re using. If the stars don’t look right, go back to PHD and make sure it’s
still guiding well (bring up the graph as shown in the image here). If it
isn’t, you’ll have to troubleshoot.

If the stars are eggs or worse, first make sure the values
you’ve entered for the guiding parameters are close to those we outlined here. One variable that can change
from night to night is the guide camera’s exposure. While mounts in this class
tend to do best with 1 – 1.5-second guide exposures, if seeing is not good a
somewhat longer one can improve guiding. There’ll be less tendency for PHD to
try to guide on movement caused by seeing.

Step Seven: Expose

Time to do what we came for, take an exposure sequence. Set the
laptop program or the intervalometer to take a number of subframes at the
exposure value you determined was best. How many? As many as possible. Even on
an easy object like M37, more subs always make for a better looking finished picture.
I generally aim for 20 - 30.

Before beginning the sequence, though, let’s put the dark
frame question to bed. Since a DSLR’s sensor chip is not cooled, dark frames
are mandatory to eliminate the false stars of thermal noise. There are two ways
to subtract dark frames from subs, manually or automatically.

If you go manual, finish the imaging run and then, just
before packing up for the night, cover the telescope objective and shoot
subframes equal in number to the maximum number of lights you’ve taken in a
sequence. For example, if you did one 20 and one 30-subframe sequence, take
30-darks. If you used different exposures on different sequences, you’ll have
to do more than one sequence of darks—dark frame exposure values need to be the
same as their corresponding lights. The darks will be subtracted from the light
frames during image processing. This way of working is certainly acceptable,
but, in addition to being labor intensive, it isn’t as effective as it could be
in my opinion.

Me, I go automatic on dark frames for a couple of reasons.
Not only do I not have to worry about messing with darks at the end of the
evening or during processing, I think automatic darks are more effective.

How do you do auto dark frames? DSLRs allow you to select a
mode called “long exposure noise reduction” (or a similarly named menu item).
Engage that, and the camera will take a dark frame after each exposure and
automatically subtract it. Yes, that means an imaging run will take twice as
long as it otherwise would—30-minutes of subs will take an hour to complete—but
I think the results are just better.

Expose!

Why would the results be improved by taking a dark after
each light? Because the temperature of the DSLR’s sensor chip will vary
throughout the night. Ambient temperature will drop throughout the evening, and,
as an exposure sequence goes on, the internal temperature of the camera due to its
electronics will tend to rise. To be most effective, a dark should be taken as
soon after its matching light subframe as possible, so the temperature it was
exposed at is close to that of the light frame.

OK, set that computer or intervalometer for the number of
exposures at the required exposure value, push the “go” button and…and…wander
around and do something else while the exposure sequence completes. I usually just
go inside and watch TV. If I’m at the dark site, I’ll cadge looks through my
buddies’ telescopes. I’ll come back periodically and see how things are
going—especially how PHD is guiding—but I rarely encounter problems unless
clouds have moved in and my guide star has been lost, temporarily or
permanently.

Once the sequence is finished, it’s time to go on to the
next target. How many targets should you do? That’s for you to decide, but I
tend to believe fewer targets, maybe just one or two per evening, and more
subframes (and maybe longer exposures) is the way to go.

Done, I’ll pack everything up and head for home if I’m at
the dark site, or, if I’m in my secure backyard, I’ll just cover the refractor and GEM with
my Telegizmos cover and only take the computer inside—which is a much more
pleasant way to end an evening under the stars than having to disassemble
everything and carry it back into the house when I’m tired.

And next? Next is processing the images, but that is a story
for some other Sunday.

Sunday, March 19, 2017

Issue #535: The Final Piece of the Puzzle

In our pre-spring observing season drive to get novices (and
maybe even a few not-so-novices) set up with a rig for deep sky imaging, we’ve
addressed mounts, telescopes, and, last week, auto-guiding setups. This Sunday
we’ll finish with suggestions for a low-cost camera. I’ve talked about imaging
cameras with y’all fairly recently, but the difference is that this time I’ll
try as hard as I can to keep the cost as low as possible.

So, you need a camera and a few accessories. Where do you
start? The first question to answer is, “Do I want color?” While a monochrome
CCD/CMOS astronomical camera can take color images by exposing successive
frames through three or more colored filters, it’s not something you want to
face when you are just getting off the ground in imaging. Unless you enter the
ranks of the hard-core someday, you may never
want to face it. In the beginning you will find just processing a “one-shot”
color image enough of a challenge. Properly calibrating and combining three +
separate frames into a color frame and then stacking and processing a bunch of
those? Uh-uh.

So, it’s a color camera, a one-shot color camera, you want.
How does one work? A color camera is different from a monochrome camera in that
red, green, and blue color filters are built into the sensor chip. Software,
either in the camera or in an image processing program, automatically combines
the R, G, and B to produce a full color image. That is usually transparent to
the user—with a digital single lens reflex (DSLR), anyway. You take a picture,
you see a color image, end of story.

Some astrophotographers say a monochrome camera can produce
visibly higher resolution images because it doesn’t waste pixels on the
production of a color image. In truth, in the beginning at least, and
especially on deep sky objects, you won’t notice any difference.

The next question is “CCD or CMOS?” That is not much of a
question today. Unless you are interested in some special applications, mostly
having to do with obtaining scientific data, there is no reason to choose a CCD
chip over a CMOS chip. Today, the formerly preferred CCD has lost ground to
CMOS sensors even for use in “astronomical” cameras. CMOS chips are now very
sensitive and very low in noise. At any rate, almost all cameras in our price
range, which I am topping out at 450 dollars, have CMOS chips, so the choice
has already been made for you.

What a ZWO ASI120MC can shoot...

Next up, cooling. “Does a camera for taking long-exposure
images need to have its sensor chilled to reduce thermal noise?” Today, probably
not. With some camera/chip combos, an internal fan, at least, can be helpful to
reduce the false stars of thermal noise, but the low-noise characteristics of
today’s sensors usually means subtracting a dark frame is enough to deal with
thermal noise.

And the Final Jeopardy Question… “Astro cam or DSLR?” There are some interesting low cost
astronomical cameras coming on line, like those from China’s ZWO, and I’ve
actually taken credible deep sky image with one of their 1/3-inch cameras that
cost a measly 200 dollars. However, I think for most of us a DSLR is just a
much more sensible choice. A much more sensible choice.

Why is a DSLR better? There are several reasons, but there
is one real big one: when you’re not
taking pictures of the night sky, you can be wowing everybody at your mother-in-law
Margie’s birthday party with your snapshotting skills. There’s also that big
elephant in the living room. Like many wannabe astrophotographers, a few nights
wrestling with camera and scope may convince you you are actually more of a visual observer. If that be the case,
you can still get years of use and enjoyment out of the DSLR, even if you never
take another astrophoto with it.

Another big plus (for astro imaging) of the DSLR? Their
relatively big chips. A less than 500 dollar camera will have an APS-C size
chip. Lower cost astro-cams tend to have small chips that restrict your field
of view, focal length for focal length, and also tend to make guiding more
critical.

Finally, while I control my DSLRs with a program running on
a laptop (“tether them,” as we say in the photography business), which makes
focusing and framing much easier, you don’t have
to do that. You don’t have to have a computer out in the field when you are
taking pictures. You can do just as we did in the SLR days: telescope, mount, camera. You will, as in those
SLR days, need a remote camera release (an intervalometer, preferably), but
that is it.

OK, so which DSLR?
The safe thing to say is still “Canon.” In some ways they still lead the pack
in astrophotography. The Canons are remarkably low in noise over long exposures,
and are easy to use in the field with a laptop if you choose to do that. Things
are changing now, but until recently camera control software (like Nebulosity)
was unheard of for other brands.

SCT Prime Focus Adapter

There’s also Canon’s longstanding involvement in our game. While
Nikon and, now, Pentax are coming on strong for astrophotography, until the
last couple of years only Canon acknowledged people were actually using their
cameras for astronomical imaging and produced cameras with astronomy in mind.

Canon is a safe choice, in my opinion, but which one of
their many DSLRs? If you are buying new and must keep the price tag low, the Rebel T6, which is available for about 450
dollars, is a remarkable value. Not
only do you get a DSLR that will perform well for astro-imaging or anything
else, you get a pretty good (zoom) kit lens for use in wide-field astrophotography
or at Margie’s above mentioned b-day party.

Just don’t want a Canon for whatever reason? The equivalent
Nikon is the D3300, which is even less expensive than the Rebel. And it can
perform very well for astronomical imaging. BUT… Computer control options for
this camera are (very) limited—it is not supported by the major Nikon
astrophotography program, BackyardNikon—so if you want to tether camera to
computer, a Canon is a far better choice.

How about buying a used camera? Is that a good idea? That
depends. A fairly recent camera or seldom used older camera can push prices
even lower. A perfectly serviceable older Rebel, like a 450D, for example, goes
for 150 or fewer dollars with a kit lens and a few accessories. Be careful
here, though. While the Rebels, Canon’s introductory DSLRs, and Nikon’s
comparable models are well-made, they are not professional grade cameras and
won’t stand up to real abuse. So, when considering an inexpensive camera it’s
best to limit yourself to one that’s for sale locally so you can examine it in
person and make sure it’s fully functional.

Accessories

Prime Focus Adapter

Prime focus adapter (1.25-inch)...

Once you’ve got a camera, of course you’ll need accessories.
You always need accessories in
astronomy, you know that! First off, you
will need a prime focus adapter in order to connect camera to telescope.
“Which” depends on your scope style. SCT prime focus adapters screw onto the
SCT’s rear port. Those for other telescope designs, like refractors, typically
have 1.25-inch or 2-inch nosepieces and slide into the scope’s focuser. I like
the 2-inch models, not because you have to worry about vignetting or something like
that with an APS-C size sensor, but because they allow me to dispense with a
1.25 – 2-inch eyepiece adapter and seem to provide a more secure mounting
arrangement.

T-ring

You’ll also need a t-adapter for your camera, aka a
“t-ring.” This is a, yes, ring shaped adapter with T-threads on one end to
screw onto the prime focus adapter, and a lens mount for your particular camera
on the other end. These two things in hand, you can remove the camera’s lens,
mount the combo of T-ring/prime focus adapter in its place, and then mount the
camera on your scope by inserting everything into the focuser or screwing the
prime focus adapter onto the rear port of an SCT.

Intervalometer

As you may know, DSLRs, most of them anyway, and certainly
all the Canons, can’t expose for more than 30-seconds without the addition of a
remote shutter release. Even if your camera could
expose for longer without a remote, you’d still want one as it allows you to
trip the shutter without bumping the scope and causing trailed stars.

T-ring

An intervalometer is a remote shutter release, but it’s also
much more. Not only will one of these (usually) wired controls allow you to trip
the shutter from a distance and expose for as long as you like, it will allow
you to shoot sequences of images. Say
30 3-minute exposures, which is exactly what we want to do. An intervalometer
allows you to do many of the things a tethered computer would allow you to do,
but without the computer. How much? A Vellois
about 50 bucks and a genuine Canon is about three times that. Guess which one I’d choose?

Memory Card

If you’re not using a tethered PC, you’ll have to have a
memory card, digital "film" on which to store your images. An SD card (used by almost all
DSLRs, now) with at least 64gb capacity is my recommendation—you’d be surprised
how much space an evening’s images can take up. Get a good, decently fast card.
I like the Sandisk ones. About 40-bucks.

Battery

If you’re going to use a battery, make sure you keep an
extra, or, better, two extras in your
gadget bag. During long exposures, the camera is drawing current from the battery
continuously, and you’re unlikely to get a full evening out of one cell,
especially on cold nights. There are lots of third party batteries available,
but I have had noticeably better performance out of genuine Canon, so that’s
what I recommend here, the real deal, for a change.

Power Supply

Yes, batteries are a problem during astrophotography, so
don’t use one, or use a real big one. Hop on over to Amazon and buy yourself
either a 12vdc or 120vac power brick for your Canon (or whatever). I do most of
my shooting at locations with mains power, so I prefer the AC option. The DC
supplies have cigarette lighter plugs that will plug right into your jumpstart
battery pack.

What do you plug one of these things into on the camera end?
These power supplies have little plastic (wired) widgets that take the place of
the normal battery in the battery compartment and supply power to the camera
that way. I’ve found one of the inexpensive—less than 15-dollars—units on
Amazon to work just fine, but Canon will sell you one for considerably more if
you like.

Anything else? Well, a few things, maybe. If you are new to
DSLR photography, you probably want a camera bag, a gadget bag, to keep camera
and lenses and, well, gadgets,
together. A nice piggyback bracket so you can mount DSLR and lens on your
telescope tube is a nice addition and you may find you like doing wide-field
shots from dark locations. A lenspen is good to keep your lens’ surface
pristine. A broadband light pollution filter can be helpful if, like me, you do
some of your imaging from an at least somewhat light-polluted backyard. And
that is really more than enough to get you started.

You’ve now got all the pieces to the complicated astrophotography
puzzle, but how the heck do you put them together? We’ll talk about that, about
getting started with all this stuff, next week.

Addendum: How good can a VX be?

Auto-guiding wise, that is. Some of you considering a
Celestron Advanced VX mount (or the similar mounts on the market today) have expressed
grave concern about my statement last week that 2” (arc seconds) of RMS guiding
error is about what you should expect of this group without some fine-tuning
(of PHD’s Brain Icon settings, I mean).

Anyhow, while 2” is perfectly suitable for some image
scale/camera pixel combos, naturally it would be nice to do a bit better with this
inexpensive and highly portable GEM. So, I set about the other night to see how
much and how easily I could tweak the VX.

Surprise! I really didn’t have to do much tweaking at all to
get this modest mount’s RMS guiding error down. I did do a decent polar
alignment, and I did spend some time carefully balancing the scope (east heavy
with a little declination bias as
well). As for the settings, I backed off on a couple of them. Cutting
aggressiveness in half and reducing hysteresis as well. Oh, and, conversely, I increased Max Duration both for RA and
declination.

The result? Despite OK but hardly great seeing, my errors
were immediately halved with me getting just under 1” of RMS error most of the
time. Even when my target got low in the sky, and seeing began to deteriorate,
the error was just over 1”, easily good enough to yield round stars with an
80mm f/6.9 despite the fairly small (1/2-inch) sensor of the camera I was testing.

While I warned you not to start chasing lower and lower
numbers with these GP/CG5 clone mounts merely for the sake of lower numbers,
given the small amount of effort involved in this substantial improvement, the
few minutes I spent was well worth it.

The other take-aways? People naturally worry about their
guide-software settings, but what makes one of the very largest differences? Seeing.
Without good seeing you will not see great guiding, so don’t start messing with
your settings on an unsteady night. Oh, and good polar alignment is important
for good guiding as well. Having to continually chase alignment-caused drift
just muddies the water and makes guiding more difficult to get right. Finally,
with this class of mounts, correct balance is just as important as polar
alignment and seeing. If you want 1” or less guiding errors, you’ll likely need
to rebalance if you move to a radically different part of the sky—cross the
Meridian, etc.

Sunday, March 12, 2017

Issue #534: Getting Your PHD

PHD2, that is, as in
America’s premier auto-guiding software. I have written about the program,
originally done by software wizard Craig Stark and now carried on as an
open-source project, a time or two before, but lots of people still have lots
of questions about it. It’s rare that my virtual mailbag doesn’t contain a
missive pleading for help with PHD.

Before offering some of that help, I suppose I should
explain what PHD2 is for the uninitiated. You’re probably more knowledgeable
than I was when I began astrophotography.
Unlike me, you know you can’t just point your telescope and camera at a
deep sky object, open the shutter, and walk away. You have to guide. The gears in most mounts are not
precise enough to allow the scope to track precisely enough over longer exposures to keep stars round
without some intervention.

To keep stars round, you watch a “guide-star” either with
the main scope or a small auxiliary telescope, a guide scope, keeping it precisely centered. Or a little camera does
that watching for you. There are some mounts that will allow you to dispense with
guiding for long exposures, but you are talking about mounts in the 10micron
class, expensive, top-tier mounts. Proletarians like yours truly guide their
mounts throughout long exposures.

How exactly do you do that guiding? Well, back in the day,
you monitored a guide star in a crosshair eyepiece in the guide scope or in an off-axis guider, and
pushed buttons on a hand-paddle—what we called our non-computerized telescope
mount hand controls—to keep the star centered. Naturally, when computers and
CCD cameras came along, we were more than happy to pass the onerous task of
guiding to them.

A guide camera is used to watch that guide star, but most
guide cameras cannot guide the telescope mount without the help of a laptop
computer and an auto-guiding program. That program is the brains of the outfit,
and that is what PHD2 is, auto-guiding software.

If you need direction on getting PHD2 downloaded, installed,
and initially configured, please see this (fairly) recent article. Today, we’re going to focus on what you need to do to get PHD2
performing by fine-tuning its default parameters. What you have to do to get
those pesky stars round.

What does “PHD” stand for, anyway? It ain't “doctor of
philosophy,” but instead, “push here dummy.” Mr. Stark’s original goal was to
produce an auto-guiding program that was as simple as it could possibly be. One
that would allow you to hook everything up, push one button and guide your way
to round star heaven. That’s actually possible in some cases, but due to the
nature of the beast, often not.

The Guiding Tab...

There are so many different possible configurations of
telescope/guide scope/guide camera/main camera/telescope mount, etc., etc. that
making a no-set-up auto-guide program is a near impossibility. Oh, if you stick
to shorter focal lengths (500mm and down) on a decent (VX and up) mount, and don’t insist on longer
than 300-second sub-frames, it is possible all you will have to do is push that
button and guide. Most of us will have to mess with PHD’s guiding parameters,
which are accessed with the program’s famous brain icon. Before we attack that,
though, a couple of preliminaries: “What is the best way to guide?” and “What
is the best guide-scope to use?”

I am frequently asked by newbies how they should guide. Should
they use an ST-4 connection, a direct connection from a camera to a mount’s
auto-guide port, or should they guide through the hand control’s serial
port? I asked myself that very thing
years ago when I first essayed auto-guiding.

Some people think serial port guiding, particularly “pulse
guiding,” a feature of some ASCOM telescope drivers, is better since each guide
message going to the mount contains not just the direction the telescope needs
to move, but also for how long. With
ST-4 guiding, once the software decides the mount needs to move, it will cause
the camera to close an electronic “switch” to move the mount. When the move is
done, the switch is opened. With pulse guiding, there is no (possible) time-lag
resulting from ST-4 mode guiding having to send an additional command to open
the switch. On the other hand, ST-4 fans say that since no back and forth
computer talking is needed with ST-4 mode guiding, it must be inherently
more responsive.

The ground truth? With my mounts/scopes/guide-cams, there
was absolutely no difference in accuracy between the two methods. The pluses
for each have more to do with convenience. If you are controlling your mount
with a computer, why not pulse guide? If you are using EQMOD in particular,
that seems a natural—everything, goto commands and guide commands, is routed
to the mount over a single cable. On the other hand, while ST-4 guiding
requires an additional cable run from camera to mount, there’s no fooling
around with serial connections and USB to serial adapters, which is a good
thing. I normally do ST-4 for that reason.

Calculating cal step size...

The other question concerns the guide-scope or lack thereof.
What sort of a guide-scope should you use? In my opinion, the answer is one
with a focal length of about 400 -500mm. That provides a fairly wide field for
small guide-cam sensor chips, but also has enough image scale for precision guiding.
The venerable Short Tube 80mm is a good choice as long as you can lock the
focuser down firmly and mount the whole thing securely to prevent
image-destroying flexure.

Me? I use a short focal length 50mm finder-guider. One of these will work up to about 1200 – 1300mm of
imaging scope focal length, and is small, light, and easy to mount firmly. For anyone
who doesn’t top 1000mm of imaging scope focal length, a finder-guider is a natural.
Having that wide field is often a blessing when it comes to choosing guide
stars.

There’s always the option of doing without a guide scope, too. Using an off-axis guider (OAG) which
intercepts a small amount of the light coming out of the main scope for
guiding. Obviously, since you are guiding through the main scope, there is no
flexure to worry about. If you are running an imaging telescope at over 1500mm of focal
length, you may find an OAG is your only workable option. The downside? You
only have access to stars at the edge of the main scope’s field, and for that
reason it can be quite difficult to find a good guide star. Luckily for me, a
long time OAG hater, I rarely image at a focal length long enough to require
one.

One final thing to discuss before we do “brain surgery.” How good does your guiding have to be?
How much error is acceptable? The answer is, “that depends.” At 1000mm or
less with an APS-C sized camera sensor chip, an RMS error of around 2” or so is
good enough. Stars will be round and small enough to please. You can even get OK (if sometimes not perfect) stars at that error level to about 1500mm of focal length.

It’s a good thing this degree of error is acceptable at the
focal lengths I use, since the plebian mounts I have in my inventory, GP
clones like we discussed last week, and the EQ-6 and CGEM mounts a step above
them, will deliver 2” of RMS error with fair ease. Getting guiding much tighter
than that with these sorts of mounts isn’t always easy and will often take considerable
experimentation.

Alright, click PHD2’s brain icon and let’s get started
entering some guide parameter values in place of the defaults, parameters than
will bring us round stars (we hope). With the brain window displayed, skip its
first two tabs, “Global” and “Camera,” since I’m assuming you’ve gone through them
in the initial program setup. Which brings us to…

Guiding Tab

The Algorithm Tab...

The first entry here is “Search Region.” This is the size of
the tracking box PHD2 draws around a star. Normally you should leave this at the
default value. If you have so much drift between guide exposures that the box
needs to be larger, you aren’t going to get anywhere with guiding anyway. The
accompanying “Star Mass Detection” has to do with PHD2 monitoring the star’s
brightness as compared to the sky background. Leave this as is as well.
Likewise, leave the tolerance setting for Star Mass Detection alone.

The next part of the window is quite important,
“Calibration.” Enter the focal length of your guide scope (you should already have
entered the size of the guide-cam’s pixels in the “Camera” tab), push the
button labeled “Calculate,” and PHD2 will figure out how long guide pulse
duration should be during calibration. The main concern here? If you have a
short focal length guide scope like I do, you need to enter a much higher
calibration step size than the default. I
have a value of 1350 here. Given the short focal length of my 50mm
finder-guider, I need that large a setting. Otherwise, calibration would take all
freaking night to complete. Leave the other stuff here alone.

The final part of the window contains things you don’t have
to worry about in the beginning. Well, except for one thing. Make sure “Enable
Guide Output” is checked, otherwise PHD2 will not issue guide commands to the
mount. It will be like that goober in the TV commercial, “I’m not a dentist; I’m
a DENTAL MONITOR.”

Algorithms Tab

Here’s where we get down to the nitty gritty, the place
where you can change the settings that really and truly affect guiding. You’ll
see that the window is divided in two, with one area for right ascension and
one for declination. Let’s begin with RA.

The first thing to set is Hysteresis. PHD2 is pretty smart;
it can remember what the last RA correction was like and use that information
in formulating the next correction. The number here is a percentage. It is how
much the remembered previous correction affects the next one. At 40%, the next RA
correction will be 40% based on the magnitude of the previous correction, and
60% on the star movement PHD2 is seeing at the moment.

Guiding Assistant...

What should you set it at? More Hysteresis yields smoother
guiding. Too much, however, and a sudden guide star movement will not be
adequately compensated for. I have my
value at 40%, which seems OK.

Coupled with Hysteresis is “Aggressiveness.” That setting is
how much (as a percentage) of the calculated necessary movement PHD2 actually
sends to the mount. The reason for this is to decrease the chance of the mount
overshooting the star, going back the other way on the next guide command, and
overshooting in that direction too, “ping-ponging.” Normal settings rage from
about 70% to 100%. I am set at 85%.

Next is “Minimum Move.” This is the amount the star is
allowed to drift without PHD2 issuing a guide command. The reason for this is
to reduce unneeded guiding corrections caused by non-tracking related star
motions due to seeing or other momentary events like mount vibration, wind,
etc. The default is .15 and that’s where
I’ve left it.

Max RA duration, the last setting on the RA side, is similar
to the above in that it’s meant to smooth out guiding, to prevent herky-jerky
guiding. This figure is in milliseconds, and limits the duration of the RA
guide command. I’ve settled on a value
of 1200 for RA through trial and error. I am thinking that is low, however, and might try a higher value next time out.

Now for the declination side of the house…

First up is “Resist Switch,” which means PHD2 tries to avoid reversing the
guide direction in declination. That is always a good thing, since in many cases issuing a guide command in dec to go back the other way will be a
problem. Star movement in declination opposite the constant slow (you hope) drift caused by polar alignment errors is usually caused by seeing,
vibration, mount flexure, wind, etc., and as with RA, we want to avoid issuing
guide commands for these things. Most of all, many mounts have considerable backlash in declination, which would create a considerable time lag between command and movement if the mount reversed direction in dec.

Also on the declination agenda are aggressiveness, minimum
move, and backlash compensation settings. I
have the first two at the same value I have for RA. The backlash
compensation option determines whether PHD2 will use a backlash compensation
value it has computed if a declination correction opposite the previous one
needs to be issued. I have this off,
since I don’t seem to be having any major dec problems.

Max Dec Duration has the same purpose as in RA, to smooth
guiding. I have my value set a little
higher here than I do in RA, 1500, but it could probably be higher still.

Finally, there is “Dec Mode.” Normally this is set to
“Auto,” which tells PHD that the occasional declination reverse guide command
(caused by whatever) is permissible. Why would you want to disallow this by
selecting “North” or “South”? If your mount has really bad declination
backlash, trying to make a “reverse” correction may cause serious problems—the
cure may be worse than the disease. I am
set to “Auto.”

And that is it, folks. The other Brain tabs cover use of
adaptive optics guiders and are of little interest to most of us.

Getting round stars with an import mount is fairly easy at 900mm...

How do you fine tune your mount if these values don’t work
for your particular setup? Trial and error, which was what I did to arrive at the numbers I’ve
given here. There is one alternative, though, PHD2’s “Guiding Assistant.” Theoretically, invoking this tool should allow the program to decide what your
guiding values should be. When the procedure has completed its work, it will
make suggestions, which you can implement or ignore at your discretion.

Alas, when I tried Guiding Assistant some time back, one
night at the 2015 Peach State Star Gaze, the figures PHD2 came up with seemed
to make my guiding worse rather than better. However, that was over a year ago,
so the Assistant may have been improved by now. If you invoke it and use the suggestions,
make sure you’ve written down your old numbers so you can get back to the way
things were if Guiding Assistant doesn’t work for you.

I hope all this stuff didn’t put you off too much. Again,
with a halfway decent mount and a reasonable focal length, you might not have
to do much with anything beyond basic setup other than just setting your
calibration step parameter. And remember, if your stars are round your stars are round. Don’t start
chasing lower and lower error values just for the sake of lower values, “The
Only Enemy of Good Enough is More Better.”

Sunday, March 05, 2017

Issue #533: A New Way to Polar Align

If you are using an equatorial mount, fork or German
equatorial, for imaging, that mount has to be accurately polar aligned. The
right ascension axis has to be pointed precisely at the North Celestial Pole or
South Celestial Pole. If it’s not, longer exposures will suffer from a
phenomenon called “field rotation,” which makes stars trail no matter how
accurate the guiding. Heretofore, there were basically two ways to polar align a
mount, the easy way or the hard way.

The easy ways? One was to use a polar borescope on a GEM.
Once you figure out how to set it up, a polar finder can yield alignments
ranging from excellent to usable depending on the borescope’s manufacturer and
your expertise in using it. For many folks kneeling on the
ground to peer through that dim little telescope in quest of a sometimes-rough polar
alignment (unless you have a Takahashi mount and its excellent polar finder) is
a bummer. Also, no truly accurate polar finder has ever been produced for fork
mount telescopes, though some people, like the late Roger Tuthill, have tried.

Another fairly easy polar alignment method is “Kochab’s Clock.” That involves lining up the RA
axis with the help of one of Ursa Minor’s stars. Kochab’s can potentially yield
a good alignment if done with care, but
in most cases, not a sub 5’ – 10’ alignment.

Finally, there is the sure
thing, a declination driftalignment,
which, unfortunately, most of us don’t consider overly easy. Or at least not overly
quick. You observe a pair of stars near the Celestial equator, and watch their
drift in declination (through the main scope) as the telescope tracks,
adjusting the mount’s altitude and azimuth controls until there is no
significant north/south drift of either star over at least five minutes of
time.

“Drifting” is not hard once you get the hang of it, but it
does take time, and you have to be able to acquire suitable stars, one near the
intersection of the Celestial Equator and the Local Meridian, and one near the
Celestial Equator and about 15 - 20 degrees off the eastern or western horizon.
That’s not always possible at every observing site.

And there things remained for years. In the 1990s, I used a
fork mounted SCT, and did a two-step polar alignment. First, I’d rough it in
using a 50mm finder scope with a polar alignment reticle. That was, as above,
not a recipe for a good alignment on a fork mount scope, but it at least got me
in the neighborhood. Then, I’d go on to drift, which took about half an hour or
so once I gained some experience. I never liked drifting, though, and for that
reason I usually quit before my polar alignment was quite good enough for the
long exposures required in the film astrophotography days.

Typical polar borescope finder reticle

Flash forward ten years or so to the coming of the
computerized GEM mounts like the Celestron Advanced GT CG5. One of the big
breakthroughs with the CG5 (and also a few other brands) was an automated polar alignmentroutine. With the CG5, you did a
three-star (no 2+4 in the firmware’s early days) goto alignment. You then
requested “Polar Alignment.” The mount would then point at Polaris, and over
the course of a couple of steps would slew away from the star. You’d then
re-center Polaris using the altitude and azimuth adjusters. While you would be
centering Polaris in the eyepiece, what you’d really be doing would be
offsetting the RA axis to place it on the true Celestial Pole about ¾ of a
degree away from Polaris (the routine also worked in the Southern Hemisphere).

This procedure didn’t produce a great polar alignment, but
it was a little better than what I could do with the CG5’s (pitiful) polar borescope,
and it was definitely quicker. It was sufficient for the short exposures at
short focal lengths I was doing with my Meade DSI CCD camera at the time.

Then came Celestron’s new polar alignment routine, AllStar
Polar Alignment, ASPA, in late 2008. This alignment procedure was different mainly
in that it allowed you to supposedly use any star (other than Polaris) for
polar alignment. We eventually found out a good ASPA star was not really any star, but a star due south and on or
lower than the Celestial Equator. Get a good star, do two iterations of ASPA,
and you’d have a close enough polar alignment for most imaging tasks.

While AllStar was not inherently more accurate than the old
Polaris system, it was coupled with the new and much more accurate 2+4 goto
alignment in Celestron’s updated firmware. With these types of polar alignment routines,
the better the goto alignment, the better the resulting polar alignment. How
accurate was/is ASPA? You’ll wind up about 10’ away from the pole or a little
better, usually, with one iteration.

The downside? If you wanted better than that 10’ or thereabouts,
you needed to do two ASPAs. That could be a bummer since you’d normally
want to do a new goto alignment after each ASPA (or at least “replace” the last
goto alignment star). If you chose to do a new ASPA after each iteration, by
the time all was said and done you’d have centered as many as 18 stars for goto alignment. The
automated StarSense alignment camera made doing two ASPAs a little more palatable, but
you’d still be spending around twenty minutes doing goto and alignments.

Nothing changed for nearly another decade, till the
enterprising Chinese CCD camera maker, QHY, came up with a new idea, which they
called “Polemaster.” I was skeptical at
first. A tiny camera not much different from my QHY-5LII guide camera save for
the addition of some wide-field optics would be mounted in place of the mount’s
polar borescope on the forward end of the RA housing. You would point the RA
axis roughly toward the pole, toward Polaris, and the cam would plate solve the
star field and tell you how to move the mount for precise polar alignment. That
seemed like a pretty tall order to me.

Polemaster camera...

How would the alignment of the Polemaster camera affect the
resulting polar alignment? How would you mount the cam if your RA axis didn’t
have provision for a polar borescope? Or you didn’t want to remove or block the
polar finder? Even if everything was perfect, how precise an alignment could a small-chip
camera like the Polemaster produce?

When I had the chance to see the Polemaster in action at the
Maine Astronomy Retreat last summer thanks to my friend Bruce Berger, all my
doubts were dispelled. The camera was completely sufficient unto its task,
producing more than enough stars in short exposures to allow it to do its job.
The real key, however, was the software. Once I had a good understanding of the
process, it was obvious what you had to do to move the mount’s RA axis to the
pole. Not just obvious, but quick. If
you are in a hurry, you could probably the entire Polemaster polar alignment in
five minutes.

Further, I later learned the mounting of the camera was not
critical. As long as it is attached to the mount somehow, someway in reasonably
secure fashion it will work. I’ve seen people use it successfully, for
example, just by duct-taping it to the mount head. Alignment is also not an
issue. The camera does not, repeat, does
not have to be finely aligned with the right ascension axis.

Watching Bruce polar align his CEM 60 quickly and precisely,
I decided this was just the solution I had been looking for. Well, it would have been save for one thing: the price. While the Polemaster is not overly
expensive, about $300.00 with an adapter for one telescope mount, that was more
than I wanted to pay given that ASPA was working pretty well for my purposes,
with its main problem being it was time-consuming and occasionally annoying.

Annoying? Yes. There’s a bug in the Celestron StarSense
firmware that sometimes causes the auto-align process to fail after the ASPA
(and StarSense requires you to do
another goto alignment after ASPA). It’s not a big deal to turn the mount off,
reset it to home position, and start another StarSense align from scratch, but
it is annoying.

Oh, and I would have liked a little better accuracy than
what ASPA produces, especially after only one iteration. For my (mainly) short
focal length, short sub imaging, I can get away with less than perfect polar
alignment, but it would still be nice to have the option of being able to
expose longer thanks to a better polar alignment.

Initially, I was hoping QHY might have pity on us and sell
their software separately. I figured my QHY-5LII would work just fine for polar
alignment in conjunction with my wide-field 50mm finder-guider. Alas, they have
not seen fit to do so; the software will only work with the Polemaster cam. So,
I continued ASPAing it. What else could I do?

Then one day a couple of weeks back, I began to hear about Sharpcap’spolar alignment tool. I was well aware
of Sharpcap itself, Robin Glover’s fantastic camera control program. Despite
its somewhat nondescript and generic name, Sharpcap is a well-respected piece
of astronomy software. It began as a tool for planetary imagers using webcams
and webcam-like cameras, but has evolved into a program that can do long exposure deep sky work easily and well. Sharpcap is compatible with just about
any camera out there as long as there is an ASCOM driver for it. Best part? Sharpcap is free.

Screen 1

Anyhow, I was told the latest release of the program,
version 2.9, included a polar alignment routine similar in concept to that used
on the Polemaster. A visit to the Sharpcap website revealed I had everything I
needed to give this Polar Alignment Tool a try:
a compatible camera (the QHY-5LII is supported natively by Sharpcap),
and that short 50mm guide scope. All I needed was one of those increasingly
rare clear nights to give it a try. I read over the instructions a time or two
in preparation, but, frankly, there isn't much to the procedure once the camera
is connected to Sharpcap. Press an onscreen button a few times, move the mount once, and
adjust the polar alignment with the mount’s altitude and azimuth adjusters.

That nice night finally came, and saw me setting up my AVX
mount and Celestron Edge 800 SCT in the backyard. Why the AVX? It’s light and I
am lazy, as I admitted not long ago. The SCT? I figured the scope’s long focal
length would serve to reveal how good Sharpcap’s polar alignment results are.
Further, I needed to take a few Moon pictures for a magazine article I am
writing, and 4000mm (with a 2x Barlow) is just right for high resolution lunar
vistas.

I put the telescope in normal “home” position, that is, pointed
north with the counterweight “down.” The QHY was inserted into the guide scope
and connected to the computer, which I positioned (temporarily) right next to
the scope so I could adjust while watching the indications on Sharpcap’s
screens.

First task was getting an image, a focused image. That was
easy enough to do (well, after I
remembered to remove the lenscap from the guide scope). Once I was close to
focus, the sensitive QHY was producing more than enough stars to meet
Sharpcap’s requirements in a mere 1.5 seconds of exposure. To work, the program
needs 15 stars within 5-degrees of the pole, and according to the information
on the first polar alignment screen, I was getting more than twice that many
despite a crescent Moon and the usual backyard light pollution.

Ready to go, I clicked Sharpcap’s Tools menu and selected
“Polar Align.” I was then presented with Screen 1, shown here. Stars marked in
yellow are the ones Sharpcap is using for plate solving the star field
(figuring out which star is which). I didn’t worry about that, just let the
program think for a little while as the frames rolled in. Shortly, the “Next”
button was enabled, meaning I was ready for step 2.

After pressing “Next,” screen 2 was presented and I was
instructed to rotate the mount 90-degrees in right ascension. I did, so, moving
the mount roughly 90-degrees to the east. Sharpcap then studied a few more
frames in order to determine where the Celestial Pole was and what I needed to
do to aim the mount there. Once it knew these things, the Next button was
enabled again.

Screen 2

After pressing Next for a final time, a star was highlighted
in yellow and there was a yellow arrow connecting it to a circle, my target . The
task was to move the mount in altitude and azimuth so as to position the star
in the little circle, not unlike what you do with a polar borescope (by the way, you don't need to return the mount to home position before adjusting; leave it rotated 90-degrees). As you
move in the proper direction, the yellow arrow gets shorter and shorter and
eventually disappears. It is then replaced with a pair of brackets around the
target to allow fine tuning. As you center the star in the target circle, the
brackets will move closer and closer together.

How easy was this to do? Quite easy AFTER I understood exactly how to do it. In the beginning, I
was fairly far from the pole, with the arrow extending off screen. I’d been
told that at this stage it was best to adjust while watching the error numbers
Sharpcap displays instead of worrying about the arrow. These numbers (degrees,
minutes, and seconds) indicate how far you are from the pole. They aren’t
labeled as altitude and azimuth; instead they read “Up/Down” and “Left/ Right.” Sounded easy to me. I’d adjust the mount’s altitude until the Up/Down
number got smaller, and the azimuth till the Left/Right went down. Alas, that
didn’t work at all.

It turned out there was a catch, and until I understood what
it was, I was all at sea. Up/Down does NOT mean the mount’s altitude, and
Left/Right does NOT equal azimuth. Instead, these error numbers relate to
directions onscreen (that's what I thought, anyway; see the addendum at the end of the article). At first I was mightily confused by the fact that moving
in azimuth changed the Up/Down distance instead of Left/Right, and vice versa.
As soon as the light went on in my head, that moving the mount’s altitude
control changed the Left/Right distance, and adjusting azimuth affected
“Up/Down,” the rest was duck soup.

In just a minute or two, I had the program indicating my
distance from the pole as under a minute in both directions, which was where I
left things. If your mount has precision altitude and azimuth adjusters, you
can get the distance lower, but the AVX’s controls, while OK, are not exactly
precise.

How long does a Sharpcap polar alignment require? Next time
out, I doubt the procedure will take any longer than the few minutes required
by Polemaster. Most of my time was, as above, spent scratching my head
wondering why adjusting altitude moved the darned Left/Right numbers.

Screen 3

The accuracy? Some night soon, I need to fire up PHD2 and
find out exactly how good Sharpcap’s polar alignment is. I know one limitation
is that I am a little close to the equator at 30-degrees north, and that since
the program does not currently take refraction into account there will be a
limit to how close it will get me. However, I will tell you it looked darned
close on this first night given the declination drift (or lack of it) of the Moon and stars
at f/20. It was obvious the alignment was at the very least as good as two
iterations of ASPA, and likely better.

Ground truth? I doubt I’ll use ASPA anymore. Now that I
understand Sharpcap’s procedure, its Polar Align Tool is just easier and, I
believe, more accurate. Sure, to do it you have to have the guide scope and
guide camera mounted on the telescope, but if you are after a precise polar
alignment you likely will be imaging and will want to guide with that guide cam
and scope anyway.

So, friends, why not bop on over to the Sharpcap website,
download the program and give it a try? Don’t cost nuttin’, and its polar
alignment feature is only one of the many good things this wonderful program offers.
At the very least, it’s made me stop wishing I had a Polemaster, and has
allowed me to keep 300 George Washingtons in my hot little hands.

Addendum: Just heard from Robin (see the comments) concerning the "direction" issue that I and some other people are having. He says that moving the polar axis up or down should indeed affect the up/down numbers. At any rate, the program works great despite the direction reversal, and what's important is to shorten that arrow, which I found easy to do once, as above, I understood what was happening.